Overview
IEC 60848:2013 defines the GRAFCET (GRAphe Fonctionnel de Commande Etape Transition) specification language for sequential function charts. Published by the International Electrotechnical Commission (IEC), this standard provides the basis for describing the behavior of the sequential part of control systems using graphical symbols and clearly defined rules for both representation and interpretation. GRAFCET is widely used within automated industrial production systems, offering a standardized way to represent the logical structure and dynamic evolution of control sequences.
This third edition of IEC 60848 is a significant update, including global technical revisions such as the extended definition of variables into internal, input, and output classes. The standard serves as a key communication tool between system design engineers, maintenance personnel, and operators, establishing a common language for the specification and documentation of automation logic.
Key Topics
- GRAFCET Language Elements: Defines specific graphical symbols for steps, transitions, directed links, actions, and variables in a function chart.
- Variable Types: Differentiates between internal variables (used within the chart, invisible externally), input variables (influencing system behavior from the environment or other components), and output variables (affected by system behavior).
- Structuring Sequential Logic: Specifies how to alternate between steps and transitions, avoiding direct step-to-step connections, and using directed links to represent evolution paths.
- Behavior Description: Details rules for initial conditions, transition clearing, evolution of active steps, and management of simultaneous operations within a control sequence.
- Input and Internal Events: Explains the role of input events (changes in input variables) and internal events (changes linked to system state) in driving sequential changes.
- Output Modes: Describes continuous and stored output modes for associating system actions with step activations or specific event triggers.
- Graphical Representation: Standardizes how to draw both simple and complex sequential structures, including cycles, parallel sequences, and structured macro-steps.
Applications
IEC 60848 is primarily applied in the following areas:
- Industrial Automation Systems: Used for the design, documentation, and verification of sequential logic in PLC-controlled processes, machinery, and automated manufacturing lines.
- Process Control: Facilitates the graphical specification of process sequences, ensuring unambiguous communication between designers, integrators, and operators.
- Design Documentation: Offers standardized graphical documentation, supporting clearer communication of system logic for maintenance, troubleshooting, and future upgrades.
- Programming Reference: Serves as a foundational specification for the implementation of sequential function charts in various programming languages, such as the SFC language of IEC 61131-3.
- Training and Education: Provides a pedagogical framework for teaching sequential logic, facilitating understanding through standardized diagrams and concepts.
Related Standards
Several international standards are relevant to IEC 60848 and its application:
- IEC 61131-3: Defines programming languages for PLCs, including the SFC (Sequential Function Chart) language, which is closely related to GRAFCET concepts.
- IEC 60050-351: Electrotechnical vocabulary, providing definitions for terms used within GRAFCET and broader automation contexts.
- IEC 61346: Classification and graphical representation of systems and their components.
- ISO/IEC Directives: Provides general rules for drafting and applying international standards.
By aligning with these standards, IEC 60848 ensures compatibility and consistency across international industrial automation projects, supporting safer, more reliable, and more efficient automated systems.
Keywords: IEC 60848, GRAFCET, sequential function charts, specification language, industrial automation, control systems, graphical representation, sequential logic, input variables, output variables, internal variables, automation standard, sequential control, process control, PLC programming.